<!DOCTYPE html>
<html>
<head>
<style type="text/css">
#red {
 height: 20px;
 background-color: red;
}
#green {
 height: 20px;
 background-color: green;
}
#blue {
 height: 20px;
 background-color: blue;
}
.margin {
 height: 20px;
}
</style>
</head>
<body>
<div id="red"></div>
<div class="margin"></div>
<div id="green"></div>
<div class="margin"></div>
<div id="blue"></div>
</body>
</html>
